Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 924.6	$ 898.9	$ 2,523.0	$ 2,513.5
Operating income (loss)	162.6	235.9	437.1	497.8
Income (loss) from continuing operations, net of tax	128.8	180.0	310.8	345.5
Loss from discontinued operations, net of tax	(0.4)	(0.1)	(2.0)	(1.4)
Net income (loss) attributable to common shareowners	128.4	179.9	308.8	344.1
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	516.2	504.6	1,385.9	1,375.8
Operating income (loss)	125.9	117.0	235.9	216.3
Net income (loss) attributable to common shareowners	114.1	116.5	191.6	180.5
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	397.0	382.6	1,106.9	1,104.4
Operating income (loss)	115.0	110.3	268.8	259.4
Net income (loss) attributable to common shareowners	69.0	68.0	158.7	152.1
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	864.3	835.8	2,209.1	2,147.5
Operating income (loss)	244.2	232.8	473.3	438.4
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	483.2	468.6	1,209.2	1,170.6
Operating income (loss)	125.9	119.4	213.8	193.6
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	381.1	367.2	999.9	976.9
Operating income (loss)	118.3	113.4	259.5	244.8
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	39.5	38.0	248.7	288.1
Operating income (loss)	(3.7)	(5.7)	27.0	28.6
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	23.9	23.1	142.6	164.1
Operating income (loss)	(1.4)	(2.9)	15.3	15.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	15.6	14.9	106.1	124.0
Operating income (loss)	(2.3)	(2.8)	11.7	13.3
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	9.4	13.4	35.0	44.6
Operating income (loss)	0.4	0.2	4.4	8.7
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	9.1	12.9	34.1	41.1
Operating income (loss)	1.4	0.5	6.8	7.4
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.3	0.5	0.9	3.5
Operating income (loss)	(1.0)	(0.3)	(2.4)	1.3
Utility Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	913.2	887.2	2,492.8	2,480.2
Operating income (loss)	240.9	227.3	504.7	475.7
Income (loss) from continuing operations, net of tax	183.1	184.5	350.3	332.6
Loss from discontinued operations, net of tax	0.0	0.0	0.0	0.0
Net income (loss) attributable to common shareowners	183.1	184.5	350.3	332.6
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	11.4	11.7	30.2	33.3
Operating income (loss)	(78.3)	8.6	(67.6)	22.1
Income (loss) from continuing operations, net of tax	(54.3)	(4.5)	(39.5)	12.9
Loss from discontinued operations, net of tax	(0.4)	(0.1)	(2.0)	(1.4)
Net income (loss) attributable to common shareowners	$ (54.7)	$ (4.6)	$ (41.5)	$ 11.5